In recent years, a diversity reception technique, which is a method of receiving electric waves by a plurality of antennas, respectively, and selecting an antenna in a best reception state, thereby increasing reception sensitivity, has attracted attention. This technique is used to avoid fading. The fading is a phenomenon in which when an electric wave propagates through a space, the electric wave is strengthened or weakened depending on a location due to interference caused by a reflected wave from a terrain or building. As the frequency of the electric wave is increased, the influence caused by the fading increases (the intensity of the electric wave is increased or decreased in a narrower range). Accordingly, the effect of diversity reception is increased. For this reason, the diversity reception technique is employed in case where an FM broadcast with a high frequency is received by a radio. On this occasion, signals received by the respective antennas are digitized for comparison. A plurality of A/D converters having the same performance thus becomes necessary (refer to Patent Document 1).
There is also a demand to increase conversion accuracy though there is no need to perform multiple receptions. Take, for example, radio reception again. Noise immunity of an AM broadcast is lower than the FM broadcast. In other words, in FM, information is represented by a change in frequency, while in AM, the information is represented by the change in amplitude. When an external noise is included, the amplitude is more influenced by the external noise or the amplitude has a lower noise immunity. Accordingly, a high signal-to-noise (S/N) ratio is required. On the other hand, the frequency of the AM broadcast is low. Thus, the effect obtained by the diversity reception is low, so that only one system of an A/D converter suffices.